Electric fuse



April 1950 A. M. POPP 2,502,747

ELECTRIC FUSE Filed July 26 1946 Pm m4wm Patented Apr. 4, 1950 ELECTRICFUSE Arthur M. Popp, Snyder, N. Y., assignor to Pierce Renewable Fuses,Inc., Buffalo, N. Y.

Application July 26, 1946, Serial No. 686,264

11 Claims.

This invention relates to electric fuses and fuse links formed toprotect an electric circuit against overloads and constructed to providea delayed action or time lag before the fuse link blows.

Fuses and fuse links have heretofore been constructed to provide arelatively long time lag at high overloads, such as 100 per centoverload and higher, so that the links will not blow at such overloadsuntil a, certain time interval or lag has elapsed, but such prior fusesand links were not designed to provide sufficiently long time lags atlower overloads. It is obvious that if a circuit is overloaded, forexample 30 per cent to 50 per cent, there is practically no danger offire and very little danger of damage to motors or other equipment inthe circuit controlled by the fuse, unless such overload continues forrelatively long periods of time, and consequently, it is objectionableto have a fuse link blow on a relatively small overload after a shortinterval of time. The fact that a fuse link may be designed for arelatively long lag at high overloads, does not ensure that the linkwill also have the required longer time lag when the circuit isoverloaded to a much smaller extent.

It is, consequently, an object of this invention to provide a fuse and afuse link which is capable of providing a relatively long time lag atlow overloads and at the same time, provide the desired time lag at highoverloads.

Another object of this invention is to provide a fuse link of improvedconstruction which is so formed as to provide better cooling of the linkwhen the same is heated due to relatively low overloads, so as toprovide an increased lag at such low overloads. A further object is toprovide a fuse link having narrow slits or notches extending inwardlyinto the link at an inclination to the longitudinal edges of the link.Another object of this invention is to provide a fuse link having one ormore portions thereof formed to provide a narrow neck of fusiblematerial extending at an angle to the length of the link. Another objectis to provide a fuse link having a section arranged between narrow necksof the fuse link and which section is providedwith diagonally extendingslots by means of which the desired cooling effect is produced whichdelays the blowing of the fuse at low overloads until such low overloadshave persisted for a relatively long period of time. A-further object ofthis invention is to provide a fuse link embodying these improvementsand which is made of a single strip of metal of substantially uniformthickness 2 throughout its length. Other objects and advantages of thisinvention will appear from the following description and claims.

In the accompanying drawings:

Fig. 1 is a sectional elevation of a fuse housing or casing having afuse link embodying this invention arranged therein.

Fig. 2 is a central sectional view thereof, on an enlarged scale, online 2-2, Fig. 1.

Fig. 3 is a face view of a fuse link of modified construction removedfrom the casing.

In the accompanying drawings are shown fuse links embodying thisinvention arranged in fuse casings of the knife blade type, but it willbe understood that the improved fuse links may be used in connectionwith fuse casings of other types. The fuse casing or housing shownincludes an outer tubular enclosing casing or shell 6 of hard fiber orother suitable insulating material, an inner shell or frame I of similarmaterial which may be open intermediate of its ends at one side thereof,that shown having the intermediate portion thereof of substantiallysemicylindrical form and the ends of cylindrical form. The removablefuse link 8 which will be hereinafter described more in detail may beinserted and removed from the frame or inner shell 1. 9 and I8 representthe usual blades of the fuse, which extend into the interior of theinner frame or shell 1 and the inner portions of these-blades formterminals H to which the ends of the fuse link 8 may be secured. Theblades 9 and ID are suitably secured to the ends of the frame or innershell 1 by any suitable means, such as pins l2 extending through thecylindrical end portions of the inner frame or shell I and also througha cupshaped member [4 arranged within each end of the frame or innershell 1 of the fuse.

The outer shell of the fuse casing is provided at one end thereof with aferrule or cap i6 rigidly secured thereto in any desired manner, forexample, by means of a screw-threaded connection and indenting portionsI! of the cap into the threaded portion of the shell 6, to lock the capagainst unscrewing from the outer shell 6. This cap or ferrule'has atits end an inwardly extending'flange' I 8 having a hole therein largeenough to permit the blade 9 to be rotated about its axis relatively-tothe ferrule. Atthe other end of the outer housing 6 a similar ferrule orcap 20 is provided having an inwardly extending flange 2| which" issuitably connected rigidly with the blade Ill. This may, for example, bedone by having the flange 2l' of the ferrule 20 extending inwardly to agreater extent than the flan e I a of the other ferrule, thus forming ahole in the end of the ferrule smaller in diameter than the blade I9 andforming notches in the flange at diametrically opposite portions thereofinto which the edge portions of the blade l may extend. Any othermounting for the blade I0 and the ferrule may be provided so that thereis no relative movement between these. parts. The cap or ferrule 20 hasan internal screw thread i9 formed to mesh with an external threadformed on the end of the outer shell 6, as clearly shown in Figs. 1 and2. Consequently, when the ferrule 20 is turned relatively to the ferruleI6 and shell 6; it will be screwed on or unscrewed from the outer shell6, to enable the fuse casing to be. readily taken apart to afford accessto the fuse link 8.

When the fuse link 8 blows,. the products. of combustion resulting fromthe blowing. of the link.

together with particles of molten metal pass in opposite directionstoward the ends of the fuse casing, and consequently, the cup members Mare provided with a series of holes v24 therein and end plates 26,secured to theends of the inner shell I also have holes 25 therein bymeans of which the-fuse is vented. Suitable screening material 28 ispreferablyprovided between these two series of holes so that any solidmatter, such as lumps or molten metal as well as flame. will beprevented from passing outwardly beyond the ends of the fuse. Theseholes in the end plate 26 and in the cup members I' l also serve toventilate the fuse while the same is in use in that heat developed inthe fuse link will tend to cause an upward circulation of air in thefuse casing, cool outside air entering through the holes in the lowerend plate 26*and the cup member M and heated airpassing out at the upperend of the fuse through corresponding holes. The screening material 28-maybe in the form of one or more layers of'finewiremesh, gauze orperforated metal. Fuse links may be clamped to the inner terminals H ofthe blades 0 and It in any suitable manner, for example, by means ofscrews 30 having a threaded engagement with nuts 3! which are suitablysecured to the terminals l I".

The improved fuse links shown in the drawings are well suited for use inconnection with fuse casings of the type described, but they may be usedwith fuse casings of other types and con structions. These links aremade of flat sheets or strips of fusible metal by stamping and arepreferably of uniform thickness throughout. The links have their endsformed to be clamped into contact with the terminals l i of the fusecasing. Two types of links are shown, the link shown in Fig. 1 beingprovided adjacent to the ends thereof with notches extending inwardlyfrom opposite side edges of the link and toward each other to formnarrow necks 36. During the use of the fuse, the fusible metal of thenecks becomes heated when electric currents close to the rated capacityof the. link pass through the same from one fuse terminal H to theother. However, the fuse terminals and blades are quite large or bulkycompared to the. fuse link 8, and consequently; heat developed in thenecks of the fuselink is readily conducted through the end portions ofthe fuse link to the terminals H and the blades which are formedintegral therewith. However, in the event that a sudden overload orexcessive flow of current through the fuse link occurs, such for exampleas would result from a short circuit, the heating of, the-necks 35 ofthe fuse link; takes place much more rapidly than the 4 I conduction ofheat from the link to the ter minals, so that the metal of the necks 36will become fused or softened so that the link breaks or blows, thusbreaking the circuit.

Between the two pairs of necks 36 at opposite end portions of the link,there is provided in the link shOWn in Fig. 1, a section 38 which is ofconsiderably greater length than width, and in this section, slots ornotches 40 are provided which extend substantially diagonally of thissection of the link. These two notches which extend from opposite edgesof the link have their inner ends spaced apart to form a neck 4| which,consequently, also extends diagonally of or at an acute angle to thelength of the link. This neck is of considerably greater cross sectionalarea than the necks" 3,6 which have been described. These two inclinednotches 40 are preferably in alinementwith each other as shown in Fig.1, so thatthe neck M is located between the inner ends thereof, but anyother arrangementof the-notches so as toform between them a neck of thedesired cross sectional area and extending crosswise or diagonally ofthe link, may be provided. inclined notches divide: the section 38 ofthefuse link into two" parts of substantial size which are capable of:absorbing and. dissipating considerable quantities of heat from the neck4! which, of course, becomes heated if: overloads of electric currentpass through. the. link. In the fuse link. shown in Fig. 1, in the eventof. low over. loads, such for example" as approximately 35 per centabove the. rating of thef-use; thei neckportion H, which is designed toblow at approximately this overload, will be kept from. blowing orfusing for a considerable period of. time, for the reason that much ofthe heat developedin the neck 4! is readily transmitted to the two pertions of the section 38 of the fuselinkr The heat developed. in thenecks 36 in low overloads is, of course, readily transmitted to theterminals, H and blades 9 and I llso that atlow overloads, the necks- 36will not become fusedor. softened-to the extent. necessary to causeblowing. of. the fuse; If, however, this relatively low overload.persists for a considerable period of. time. so. as. to possiblyendanger the circuit controlled by the. fuse or any apparatus inclinedin. the. circuit, then eventually after the. two. parts of thesections38 have acquired a temperature at which. they can no longerabsorb sufficient heat from the neck 4 l the neck 4| will become fusedor softened to produce a break in the link, thus interrupting the flowof current through the fuse link- When the fuse link is subjected tohigher overloads, the softening or melting of the neck 4| takes place incorrespondingly shorter periods of time.

By arranging the slots or notches 4t and also the neck 4! at: aninclination to the length of the fuse link, the delayed fusing action ofthe neck 4'!" at low overloads is greatly improved. Numerous tests havedemonstrated this superior action of this link with. low overloads andhave demon-- strated the superiority of this link over other linkshaving slots and necks formed in various different ways therein. It"has. even been shownby' tests that if" in place cf'the inclined ordiagonally extending slots or notches and diagonally extending necks,two notchesof lengths equalto the lengths of the inclined notches areprovided spaced apart and extendingtransversely' of" the length, thatthe links with the inclined slots and necks are greatly superior for lowoverload lag. For example, the lag in a link ofthe type shown in Fig. lof'the drawing; ra-ted at 30' amperes at 250 volts, after an overload ofper cent in excess of the rated current of this fuse link was 16 minutesand 9 seconds, whereas the corresponding lag with a link of anothermanufacture of the same capacity or rating was 4 minutes and 19 seconds.

Fuse links of larger capacity for use in larger fuse casings may beconstructed as shown in Fig. 3, in which the link is provided with twooppositely disposed notches adjacent each end thereof which terminate atnecks 46. relatively small in size and will fuse or soften I'hese necksare so as to break the circuit through the link when the same issubjected to an extremely heavy overload, such as would be caused by ashort circuit.

'This link has two sections 48 similar to the section 38 of the linkshown in Fig. l, the sections 48 terminating in necks 49 connecting witha section 50, the two necks 49 being each produced by a pair oftransversely extending slots or notches 5 i. The two sections 48' areprovided with notches 53 extending at an acute angle to the length ofthe link and leaving relatively narrow diagonally extending necks 54between the angugonally extending necks 54 at the angularly extendingslots or notches are larger in cross section than the necks 49 and arenot expected to become fused during normal operation of the fuse links.In the link shown in Fig. 3, the two sections 48 having the angularlyextending notches therein are depended upon for dissipation of heatgenerated in the necks 49 during continued low overloads. Links of thetype shown in Fig. 3 have been found equally effective in prolonging thelag on low overloads. For example, a ampere 250 volt link of this typetested on a 35 per cent overload, i. e., on amperes, blew 53 minutes and4 seconds after application of the overload, whereas a link of anothermake not having the inclined notches therein and also rated 100 amperesat 250 volts, when carrying a current of 135 amperes blew in 36 minutesand 5 seconds after application of this load. Numerous other tests haveclearly shown that the inclined notches and necks have a very pronouncedeffect upon the lag of links of this type at relatively low overloads.

Each notch extends in an approximately diagonal direction as shown inthe drawings with reference to the section of the link in which thenotch is located and the acute angle formed by the notch with the sideedge of the fuse link is ap roximately from 30 to 60 degrees. The anglewhich provides the most desirable lag depends on many factors, includingthe size and thickness of the link, the current carrying capacity of thesame, the voltage, the construction of the fuse housing and others.

The ends of the fuse links which are to be secured to the terminals of afuse casing may be of any suitable or desired form, those shown in Figs.1 and 3 being provided at one end with a longitudinal slot and at theother end with a transverse slot for cooperation with the screws 30, butthe ends of the fuse links may be of any other suitable or desired formfor connection with various types of terminals of fuse casings.

The reason for this improved action of fuse links with inclined notchesand inclined necks is not deiintely known, but a greatly improved actionresults from the use of the inclined notches, regardless of whether theinclined notches form between them a neck which will blow at relativelylow overloads, as in Fig. 1, or whether these necks are at one or bothends of sections of the fuse link in which the inclined notches arelocated, as in Fig. 3.

While the fuse links shown and described have particularly desirable lowoverload lag features, these fuses also provide approximately the sameor slightly less lag than heretofore provided at higher overloads. Thisis desirable, since there is more danger to electrical apparatus orother devices on a circuit and more danger of fire from a heavilyoverloaded circuit. Tests have also shown that while the improved linksherein disclosed produce a longer time lag at low overloads when thelinks are arranged in any type of casing, yet the best results areobtained when these links are used in ventilated casings, such as theone illustrated in Figs. 1 and 2.

I claim:

1. A fuse link for providing an extended time lag at low overloads,comprising a strip of fusible metal having means at its ends forconnecting the link in an electric circuit, said link having a sectionwhich is connected with other portions of the link by relatively narrownecks, said section having substantially parallel sided notchesextending into said section in a direction sub stantially diagonal withreference to said section.

2. A fuse link for providing an extended time lag at low overloads,comprising a strip of fusible metal having means at its ends forconnecting the link in an electric circuit, said link having a sectionwhich is connected with other portions of the link by relatively narrownecks, said section having a relatively narrow notch formed therein andextending from an edge portion of said link into said section in adirection substantially dia gonal with reference to said edge portion,the edges of said notch extending substantially parallel to each other.

3. A fuse link for providing an extended time lag at low overloads,comprising a strip of fusible metal having means at its ends forconnecting the link in an electric circuit, said link having a sectionwhich is connected with other portions of the link by relatively narrownecks, said section having a relatively narrow notch formed therein andextending from an edge portion of said link substantially diagonallyinto said section and dividing said section into two parts andterminating at the inner end thereof in a neck connecting said two partsof said section and extending at an inclination to the length of saidlink.

4. A fuse link for providing an extended time lag at low overloads,comprising a strip of fusible metal having means at its ends forconnecting the link in an electric circuit, said link having a sectionwhich is connected with adjacent portions of the link by relativelynarrow necks, said section having a pair of relatively narrow notchesextending inwardly from the opposite side edges of said link and in adirection substantially diagonal with reference to said section andterminating adjacent to each other to form a neck in said section.

5. A fuse link for providing an extended time lag at low overloads,comprising a strip of fusible amen r7 metal: having means at its endsfor connectin the link in an electric circuit, saidv link having asection which is connected with other portions ofthelink. by relativelynarrow necks, said section, having a pair of relatively narrow notchesextending inwardly from, the opposite edges of said link in a directionsubstantially diagonal of said section and terminating adjacent to eachother tov form a neck in said section, said neck extending at an angleto the length of said link.

6. A fuse link for providing an extended time lag at. low overloads,comprising a strip of fusible metal having means at its ends forconnecting the, link in an electric circuit, said link having a sectionwhich is connected with other portions of the link by relatively narrownecks, said section having a pair of parallel sided notches ex tendinginto the. same from opposite edges of said link ina directionsubstantially diagonal of said section and arranged substantially inalinement with each other, and spaced apart to form between the innerends of said notches a relatively narrow neck.

7. A, fuse link for providing: an extended time terially greater lengththan width and having 3 notches formed, therein extending toward eachother from opposite side edges of said link in a directionsubstantially. diagonal of said middle section, and. forming betweenthema neck in said section, said neck being. of such cross section that itwill become. softened by currents in ex cessof the rated capacity ofsaid fuse link, the parts of said section at opposite sides of said lastmentioned notches serving to. cool said last mentioned. neck to providean extended time lag at low overloads.

8,, A fuse, link for providing an extended time lag at low overloads,comprising a strip of fusible. metal having means at its. ends. forconnecting. thelink in an. electric circuit, and hav ing a pair ofsections of materially greater length thanv width,,one of said sectionsbeing arranged adjacent to each. end of said link, said link havingnotches therein separating said ends from said sections, and a middle.section spaced from said first mentioned sections. by narrow necks, saidfirst mentioned sections each having a notch therein. extending from anedge of said link in a direction. substantially diagonally thereof.

9. A fuse linkfor providing an extended time lag at low overloads,comprising a, strip of fusible, metal having means, at its. ends; forconconnecting, the link in; an. electric; circuit, and having a pair of.sections, of. materially greater length than width, one of. saidsections being arranged adjacent to each end of said link, said linkhaving notches therein separating said ends from said sections, and amiddle section. spaced from said first mentioned sections by narrownecks, said first mentioned sections each, having apair of substantiallyparallel sided notches extending from the edge portions of said, linksub stantially diagonally with reference to said sec.- tions anddividing said sections into two portions separated by a neck.

10. A fuse. comprising a casing of substantially tubular form. andhaving openings at the opposite. ends thereof for ventilating said fusecasing, terminals extending into the. opposite: ends of said casing, anda fuse link of fusible meta-l formed to be connected to said; terminals,said link having narrow necks adjacent, to said terminals formed to blowat heavy, overloads,,-the sec tion of said link; between: said necks.havingv a relatively narrow notchformed therein, and ex;- tending, froman edge portion of said link into said section in a direction.substantially diagonally thereof, said notchterminating in a neck whichis wider than: said first mentioned necks and formed to blow when saidlink. is. subjected to moderate. overloads for extended periods of time.

11. A fuse linkv comprising a stripv of fusible metal having its endsformedfor. connecting; the link in an electric circuit, said linkhaving. a neck portion oi, materially less cross sectional area thanother portions of the link, and, anotch arranged in said link andterminating at, one end at. said neck portion and arranged diagonally tothe length of the link, said notch having substantially parallel sides.and, extending, at an. angle of not more than 60 degrees; to. the lengthof, said link.

ARTHUR M.. POPE.

REFERENCES CITED The following references are: of record in the file ofthis patent:

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1,439,870 Conant Dec..2.6., 1922 2,028,720 La Mar Jan. 21, 19.362,181,825 Wood Nov. 28, 1939. 2,287,553 Floten June 23,1942

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